To enable the transfer of extremely high mechanical loads in structural components made of fiber-reinforced plastic (FRP) composites, the use of increasing wall thicknesses is unavoidable. However, this increase leads to a reduction in the mechanical properties related to the cross-sectional area, which is due to various manufacturing-related defects such as fiber displacements and undulations. To minimize or avoid such defects, the manufacturing process must be well controlled. However, this requires precise process knowledge, especially of the flow front, which currently can only be obtained via simulative approaches.
The focus of this paper is on real-time flow front monitoring in a high-pressure resin transfer molding (HP-RTM) mold using phased array ultrasonic testing (PAUT). For this purpose, investigations were conducted during the production of test specimens made of glass fiber reinforced polyurethane resin with a wall thickness of 10 mm and a fiber orientation of ±45°. A phased array ultrasonic probe was used to record individual line scans over a period of 200 seconds. By using different measuring positions of the phased array probe and thus the line scan, an approximate two-dimensional monitoring of the polyurethane flow front can be performed.
With these results, it is possible to determine the local flow velocities of the matrix system during mold filling, which have a significant influence on the occurrence of fiber disorientations in FRP, especially in the HP-RTM process. Furthermore, these results can be used to improve the prediction quality of conventional simulative methods for determining flow velocities.